A typical fuel system as disclosed in U.S. Pat. No. 5,044,344 for an internal combustion engine of an automobile has a fuel pump module in a fuel tank connected by a fuel delivery line to the fuel rail and injectors of the engine. Fuel systems of this type do not have any fuel return line from the rail or injectors to the fuel tank and hence are often referred to as a no-return fuel system.
In a no-return as well as in other types of fuel systems, it is desirable to reduce the number of fuel passages, which thereby reduces the number of possible failure modes or leak paths. It is also desirable to reduce the number of parts in a fuel system to simplify the assembly process, to reduce cost and to reduce the size and weight of components.
In some engines, it is desirable to vary the fuel pressure at the injectors under different operating conditions. In this type of engine, the fuel injectors require a substantially higher fuel pressure at full throttle than at idle. When such an engine rapidly goes from full throttle to idle, the injector fuel pressure should be reduced immediately to avoid an overly rich fuel-to-air mixture which would result in poor engine performance and excessive engine exhaust emissions. In "hot soak" conditions, it is common for the fuel pressure to be substantially greater than that required under normal operating conditions.